Membrane, falls, bandaging and the inspection points that stop a bathroom rebuild twelve months later.
A bathroom that fails rarely fails at the tile. It fails behind the tile — at a corner that was not bandaged, a fall that ran the wrong way, or a membrane applied at half the coverage rate. Waterproofing is the least visible and most expensive-to-fix part of a bathroom, so it is worth understanding before the tiler arrives.
The standards that apply
Domestic wet-area waterproofing in Australia is covered by AS 3740 (Waterproofing of domestic wet areas) and membrane products are assessed to AS/NZS 4858 (liquid-applied waterproofing membranes). Your tiler and waterproofer should be working to these, and your building surveyor or inspector can hold them to it.
Requirements differ between a shower over a bath, a hobless shower, and a bathroom on a timber floor versus a concrete slab — so confirm the specific detail for your situation rather than assuming a generic approach applies.
Order of works
- Substrate — the floor and wall substrate is finished, stable and dry enough to receive membrane.
- Falls — the floor is screeded to fall to the waste before waterproofing. Waterproofing is not a substitute for a fall; ponding water sitting on a membrane will still find a way out.
- Priming — prime per the membrane manufacturer’s instructions. Skipping primer on a dusty substrate is a common cause of delamination.
- Bandaging — reinstate all junctions: wall-to-floor corners, wall-to-wall corners, penetrations for the waste and mixers, and the hob or step-down.
- Membrane — apply in at least two coats, in different directions, at the coverage rate on the tin. Coverage rate is not a suggestion; it is what the product was tested at.
- Curing — respect the recoat and cure times before flood testing or tiling.
- Flood test — plug the waste, fill to just below the hob or threshold, and leave it for the period your inspector requires (commonly 24 hours). Check for any drop in level.
- Protection — protect the membrane from foot traffic and dropped tools until tiling.
Where showers actually leak
- The corners — the wall-to-floor junction is the highest-movement joint in the room and the most common failure point.
- The waste — the penetration through the membrane. If it is not properly bandaged and clamped, water tracks around it.
- The hob or threshold — a timber hob that was not waterproofed over the top willwick water into the framing.
- Screw penetrations after waterproofing — every fixing through a membrane is a hole. Screen fixings and tap penetrations need sealing.
- The wrong fall — water pooling in a corner, silently, for a year.
Shower walls: how high?
Shower walls are waterproofed well above head height — to the greater of the specified height above the floor or a set distance above the shower outlet. Where a shower head is over a bath, the surrounding wall treatment is different again. Ask your waterproofer to state the heights they are working to; it is a specific number, not a judgement call.
Documentation — ask for it
Ask for, and keep:
- The waterproofing certificate from the licensed waterproofer.
- The product name and batch of the membrane used.
- Photographs of the membrane before tiling, including the corners and waste — this is the only record you will ever have of what is now behind tile.
If a leak appears in three years, that folder is the difference between a warranty claim and a full bathroom rebuild at your own cost.
Choosing tiles for a wet area
Once the waterproofing is right, tile choice is about grip and grout. Ask for the slip classification under AS 4586 appropriate to a shower floor, and remember that the same tile in a matt finish will behave differently to its polished twin.
See it in person: full slabs, large-format porcelain and engineered oak are on display at our Springvale showroom. Book a visit and bring your plans — we will measure your layout against the actual slab before you commit.